Mylan Inc. is predicting strong growth over the next several years as demand for lower-cost generic medications accelerates around the world. John Sheehan, chief financial officer of the Cecil-based maker of generic and specialty drugs, told analysts and institutional investors Thursday that Mylan will reach adjusted profit of $6 a share by 2018, which would be more than double its per-share adjusted earnings of $2.89 last year. “Our growth has been massive, and it will continue over the next five years,” Sheehan said at the Invest Pennsylvania Equity Conference in the David L. Lawrence Convention Center, Downtown.